1. Field of the Invention
The present invention relates to a sheet processing apparatus that receives and processes sheets discharged from an image forming apparatus, and an image forming system including the image forming apparatus and the sheet processing apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus such as a copying machine has fixing rollers that fix toner on a recording sheet and discharge rollers that are disposed downstream of the fixing rollers in a sheet conveying direction to discharge the recording sheet. The fixing rollers and the discharge rollers are controlled to rotate at different rotational speeds. The rotational speed of the discharge rollers is set to be higher than that of the fixing rollers. This is to prevent a sheet having absorbed heat on the fixing rollers from shrinking when it is self-cooled.
The conveying force of the discharge rollers is set to be smaller than that of the fixing rollers in order to prevent the sheet from being pulled from the fixing rollers at the rotational speed of the discharge rollers. Thereby, the fixing process is properly performed by conveying a sheet at the rotational speed of the fixing rollers. Therefore, the sheet is prevented from being pulled in such a way as to slide on the fixing rollers, and is conveyed at a conveying speed based on the rotational speed of the fixing rollers insofar as it is held by the fixing rollers.
After the trailing end of the sheet is released from the fixing rollers, the sheet is conveyed only by the discharge rollers. Hence, the sheet is conveyed at a higher conveying speed than the conveying speed at which it is conveyed by the fixing rollers.
However, in a case where the image forming apparatus is equipped with a sheet processing apparatus that receives and processes sheets discharged from the image forming apparatus, second discharge rollers of the sheet processing apparatus are provided downstream of the discharge rollers of the image forming apparatus in the sheet conveying direction. Thus, depending upon the length of a sheet, there can be timing in which the sheet is held by the fixing rollers, the discharge rollers of the image forming apparatus and the second discharge rollers of the sheet processing apparatus at the same time while the sheet is being conveyed. In such an event, if the second discharge rollers of the sheet processing apparatus rotate at the same rotational speed as the discharge rollers of the image forming apparatus, the second discharge rollers run idle since the sheet is conveyed at a conveying speed based on the rotational speed of the fixing rollers, whereby the sheet can be injured.
Further, in a case where the rotational speed of the second discharge rollers is equal to that of the fixing rollers, the sheet is conveyed by the discharge rollers and the second discharge rollers after the trailing end of the sheet is released from the fixing rollers. Since the rotational speed of the discharge rollers is higher than that of the second discharge rollers, the sheet becomes curved, i.e. the sheet is formed into a loop between the discharge rollers and the second discharge rollers. The formation of the loop deteriorates the conveying accuracy, skews, wrinkles, damages, and jams the sheet, and causes other problems. Further, the formation of the loop causes poor alignment of sheets housed in the sheet processing apparatus.
It is therefore an object of the present invention to provide a sheet processing apparatus, and an image forming system having an image forming apparatus and the sheet processing apparatus that are capable of preventing sheets conveyed to the sheet processing apparatus from being skewed, wrinkled, damaged, or jammed, and prevent sheets stored in the sheet processing apparatus from being misaligned.
To attain the above object, in a first aspect of the present invention, there is provided a sheet processing apparatus that receives a sheet discharged from an image forming apparatus comprising first conveying means for conveying a sheet on which is formed an image at a first conveying speed and with a first conveying force, second conveying means disposed downstream of the first conveying means in a sheet conveying direction, for conveying the sheet at a second conveying speed higher than the first conveying speed and with a second conveying force smaller than the first conveying force, and determination means for determining whether a trailing end of the sheet has been released from the first conveying means, the sheet processing apparatus comprising third conveying means for conveying the received sheet, and conveying speed setting means for setting a conveying speed of the third conveying means to the first conveying speed while the sheet is being conveyed by all of the first conveying means, the second conveying means, and the third conveying means, and for setting the conveying speed of the third conveying means to the second conveying speed after the determination means determines that the trailing end of the sheet has been released from the first conveying means.
Preferably, the conveying speed setting means sets the conveying speed of the third conveying means to the second conveying speed when the determination means determines that the trailing end of the sheet has been released from the first conveying means before a leading end of the sheet reaches the third conveying means.
Also preferably, the conveying speed setting means is responsive to release of the trailing end of the sheet from the second conveying means, for setting the conveying speed of the third conveying means to a third conveying speed higher than the second conveying speed.
In a preferred form of the first aspect, the first conveying means comprises fixing means for fixing an image on the sheet while conveying the sheet.
In another preferred form of the first aspect, the sheet processing apparatus comprises an original reading apparatus that reads an original, provided at an upper side of the image forming apparatus, and the sheet processing apparatus is provided between the image forming apparatus and the original reading apparatus.
According to the first aspect of the present invention, there is provided a sheet processing apparatus that is comprised of third conveying means for conveying the received sheet, and conveying speed setting means for setting the conveying speed of the third conveying speed to the first conveying speed while the sheet is being conveyed by all of the first conveying means, the second conveying means, and the third conveying means, and for setting the conveying speed of the third conveying means to the second conveying speed after the determination means determines that the trailing end of the sheet has been released from the first conveying means. As a result, it is possible to prevent the sheet from being skewed, wrinkled, damaged, jammed, or the like, and prevent sheets stored in the sheet processing apparatus from being misaligned in both of the cases where it is being conveyed all of the first, second and third conveying means and where the trailing end of the sheet has been released from the first conveying means.
To attain the above object, in a second aspect of the present invention, there is provided a sheet processing apparatus that receives a sheet discharged from an image forming apparatus comprising first conveying means for conveying a sheet on which is formed an image at a first conveying speed and with a first conveying force, second conveying means disposed downstream of the first conveying means in a sheet conveying direction, for conveying the sheet at a second conveying speed higher than the first conveying speed and with a second conveying force smaller than the first conveying force, and determination means for determining whether a trailing end of the sheet has been released from the first conveying means, the sheet processing apparatus comprising third conveying means for conveying the received sheet, and conveying speed setting means for setting a conveying speed of the third conveying speed to the first conveying speed or the second conveying speed according to information on a size of the sheet received from the image forming apparatus.
Preferably, the conveying speed setting means sets the conveying speed of the third conveying means to the second conveying speed when a sheet length indicated by the information on the size of the sheet received from the image forming apparatus is smaller than a predetermined length, and the conveying speed setting means sets the conveying speed of the third conveying means to the first conveying speed when the sheet length indicated by the information on the size of the sheet received from the image forming apparatus is equal to or greater than the predetermined length.
Also preferably, when the conveying speed of the third conveying means is set to the first conveying means, the conveying speed setting means sets the conveying speed of the third conveying means to the second conveying speed after the determination means determines that the trailing end of the sheet has been released from the first conveying means.
Further preferably, the conveying speed setting means is responsive to release of the trailing end of the sheet from the second conveying means, for setting the conveying speed of the third conveying means to a third conveying speed higher than the second conveying speed.
According to the second aspect of the present invention, the sheet processing apparatus is comprised of the third conveying means for conveying the received sheet, and the conveying speed setting means for setting the conveying speed of the third conveying means to the first conveying speed or the second conveying speed according to the information on the size of the sheet received from the image forming apparatus. As a result, the third conveying means is capable of conveying the sheet at the conveying speed that is suitable for the size of the sheet. This prevents the sheet from being skewed, wrinkled, damaged, jammed, or the like, and prevent sheets stored in the sheet processing apparatus from being misaligned.
Preferably, the determination means comprises a sensor disposed upstream of the first conveying means in the sheet conveying direction.
In this case, a period of time U required after the determination means determines that the trailing end of the sheet has been released from the first conveying means and before the conveying speed setting means sets the conveying speed of the third conveying means to the second conveying speed is expressed by:
U=L2/v
where L2 represents a distance from the sensor to the first conveying means, and v represents the first conveying speed.
To attain the above object, in a third aspect of the present invention, there is provided an image forming system comprising an image forming apparatus, and a sheet processing apparatus, wherein the image forming apparatus comprises first conveying means for conveying a sheet on which is formed an image at a first conveying speed and with a first conveying force, second conveying means disposed downstream of the first conveying means in a sheet conveying direction, for conveying the sheet at a second conveying speed higher than the first conveying speed and with a second conveying force smaller than the first conveying force, and determination means for determining whether a trailing end of the sheet has been released from the first conveying means, and the sheet processing apparatus is a sheet processing apparatus according to the first aspect.
To attain the above object, in a fourth aspect of the present invention, there is provided an image forming system comprising an image forming apparatus and a sheet processing apparatus, wherein the image forming apparatus comprises first conveying means for conveying a sheet on which is formed an image at a first conveying speed and with a first conveying force, second conveying means disposed downstream of the first conveying means in a sheet conveying direction, for conveying the sheet at a second conveying speed higher than the first conveying speed and with a second conveying force smaller than the first conveying force, and determination means for determining whether a trailing end of the sheet has been released from the first conveying means, and the sheet processing apparatus is a sheet processing apparatus according to the second aspect.
The above and other objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.